The present invention relates to an automatic analysis apparatus having a function for pipetting a liquid sample from one container to another container by using a pipetting probe that serves as an electrode for detecting liquid level.
In a conventional automatic analysis apparatus, the liquid sample of a living body such as blood or urine is pipetted from a sample cup to a reaction container on a reaction line, a reagent is pipetted from a reagent bottle to the reaction container corresponding to analysis items of measurement objects, and the mixture of the sample and the reagent is measured by a measuring means such as a photometer.
In the pipetting operation, the tip of the pipetting probe is dipped in the sample liquid of the pipetting object, but the deeper that the tip of the pipetting probe is dipped, the greater than the quantity of the sample liquid adhered to an outer wall of the probe increases, and the contamination becomes significant.
Then, in order to reduce the dipping depth of the pipetting probe as much as possible, a liquid level of the container is detected, and at a position where the tip of the probe reaches a little beneath the liquid level, the probe stops to move down, and the probe is controlled to withdraw a predetermined amount of the sample liquid.
A pipetting probe serves as an electrode for detecting liquid level, and a liquid container holding means serves as the other electrode for detecting liquid level; the liquid level in the container is detected by a change of an electrostatic capacitance between the pipetting probe and the liquid container holding means, as shown in Japanese Patent Laid-open No. 62-289769 (1987) bulletin and Japanese Patent publication No. 6-7112 bulletin (corresponding to U.S. Pat. No. 4,897,244).
In these documents, the pipetting probe is connected to an electric liquid level detecting circuit, and the liquid container holding means is electrically connected to the ground.
Furthermore, relating to the pipetting probe having a metal inner tube and a metal outer tube, Japanese Patent Laid-open No. 7-43369 bulletin is disclosed, in which insulation resistance between the metal inner tube and the metal outer tube is kept in a good condition, whereby the electrostatic capacitance corresponding to the liquid level of the sample is surely detected.
Further relating to a pipetting nozzle serving as one electrode to detect the liquid level of the sample, Japanese Patent Laid-open No. 8-258661 bulletin is disclosed.
In the automatic analysis apparatus stated above, the sample cup pipetted with the sample liquid corresponding to the pipetting object is mounted on a sample disc as one embodiment of the container holding means.
When all of the sample cups are set to the sample disc, a detecting signal on the basis of the change of the electrostatic capacitance between the pipetting probe and the sample disc is a big value, and the liquid level detection error is very small.
On the other hand, several kinds of the sample cups having different size are used usually. An especially small sample cup may be set on the sample disc directly, and other containers or supporting holding tools are set on the container loading region of the sample disc, or the small sample cup may be mounted indirectly on the top of the other containers or the supporting holding tools.
When a small-sized sample cup having a short overall length is set on the sample disc indirectly, the spatial distance between the sample liquid in the sample cup and the sample disc serving as the electrode for detecting liquid level becomes large, and it becomes impossible to obtain a sufficient detecting signal to recognize the liquid level with which the pipetting probe contacts, such that the liquid level detection is not executed surely.
An object of the present invention is to provide an automatic analysis apparatus which is capable to surely detect a liquid level of the sample liquid of the sample cup, even if the height of the sample cup is different from the height location arranged for the sample cup holding means.
In the automatic analysis apparatus comprising a pipetting device for pipetting a sample liquid from a sample cup to a reaction container by using a pipetting probe that serves as an electrode for detecting a liquid level of the liquid sample, the sample cup holding means serving as another electrode for detecting the liquid level, an electric detecting element for detecting a change of an electrostatic capacitance between said pipetting probe and said sample cup holding means and a measurement means for measuring the contents of the reaction container, the present invention is characterized by comprising a construction such that a conductive material is arranged along a direction to which the pipetting probe is disposed, and said conductive material has an isopotential to the other electrode.
In a desirable embodiment of the present invention, said sample cup holding means are driven so as to transfer said sample cup being held to an aspiration location by said pipetting probe, and said conductive material is arranged apart from said sample cup holding means and in the neighborhood of said sample aspiration location.
This conductive material includes a pair of plate portions which oppose each other, keeping a gap through which said sample cup on said sample cup holding means is able to pass.
Said sample cup holding means and said conductive material are contacted to ground electrically.
In a desirable embodiment of the present invention, a control part is provided for controlling moving down operation of the pipetting probe according to the output of the liquid level detecting signal supplied from an electric circuit based on change of an electrostatic capacitance between the pipetting probe and the conductive material.
The conductive material is arranged in a region between a height location that is lower than a bottom end of the probe when the pipetting probe moves to a horizontal direction and a height location that is higher than the upper end of sample cup holding means.
This conductive material has a part extended in parallel to a direction to which the pipetting probe moves down.
Moreover, the sample cup holding means has an electrical conduction body as another electrode which surrounds the outer wall of the sample cup.